Float volt_x=analogread (A0); // Vin Input
    Float volt_in=5*(volt_x/1023);
   
    float rx=(volt_in*100000)/(5-volt_in); // ---------- >>>>>> Resistance Formula
    float rx_divided=rx/1000; // ohm ----> k ohm
   
If the value read by the analogread command is placed in the formula, the resistance value is found.
We convert this value primarily to the type of string variable and then to the series-jar type. And with the following command line, we send a Bluetooth modular.

Flutter-Dart codes were used for the Android program. Flutter-Dart and Arduino codes below.

Flutter-Dart Codes:

import 'dart:async';

import 'dart:convert';

//import 'dart:convert';

import 'package:flutter/foundation.dart';

import 'package:flutter/material.dart';

import 'package:flutter_bluetooth_serial/flutter_bluetooth_serial.dart';

void main()=> runApp(const MyApp());

class MyApp extends StatefulWidget {

  const MyApp({super.key});

  @override

  // ignore: library_private_types_in_public_api

  _MyAppState createState()=> _MyAppState();

}

class _MyAppState extends State<MyApp> {

  List<BluetoothDevice> _devices=[];

  late BluetoothConnection connection;

  String adr="00:21:07:00:50:69"; // my bluetooth device MAC Adres

  String recData="0 ohm";

  late Timer _timer;

  String _timeString="";

  @override

  void initState() {

    // _startTimer();  automatic

    super.initState();

    _loadDevices();

  }

  Future<void> _loadDevices() async {

    List<BluetoothDevice> devices=await FlutterBluetoothSerial.instance

        .getBondedDevices();

    setState(() {

      _devices=devices;

    });

  }

  //----------------------------

  Future<void> sendData(String data) async {

    data=data.trim();

    try {

      List<int> list=data.codeUnits;

      Uint8List bytes=Uint8List.fromList(list);

      connection.output.add(bytes);

      await connection.output.allSent;

      if (kDebugMode) {

        // print('Data sent successfully');

      }

    } catch (e) {

      //print(e.toString());

    }

  }

  // data RECEIVED --------------

  Future<void> receiveData() async {

    connection.input!.listen((Uint8List data) {

      //Data entry point

      setState(() {

        recData=ascii.decode(data);

        //var n1=int.parse('-42');

      });

    });

  }

  //--------------------------------------

// TIMER START-----------

  void _startTimer() {

    _timer=Timer.periodic(Duration(milliseconds: 500), (timer) {

      receiveData();

    });

  }

  // TIMER STOP--------------------------------------

  Future<void> _stopTimer() async {

    setState(() {

    });

    _timer.cancel();

  }

//---------------------------------------------

  @override

  void dispose() {

    _timer.cancel();

    super.dispose();

  }

  @override

  Widget build(BuildContext context) {

    return MaterialApp(

        home: Scaffold(

          appBar: AppBar(

            title: const Text("OHMMeter with BlueTooth"),

          ),

          body: Center(

            child: Column(

              mainAxisAlignment: MainAxisAlignment.center,

              children: [

                const Text("MAC Adress: 00:21:07:00:50:69"),

                ElevatedButton(child: Text("Connect"), onPressed: () {

                  connect(adr);

                },),

                const SizedBox(height: 30.0,),

                const Text("Receive Data: ",style: TextStyle(fontSize: 55.0),),

                Text(recData,style: TextStyle(fontSize: 45.0),),

                const SizedBox(height: 10.0,),

               // Text(_timeString),

                const SizedBox(height: 10.0,),

                ElevatedButton(child: Text("Stop timer"), onPressed: () {

                  _stopTimer();

                },),

                const SizedBox(height: 10.0,),

                ElevatedButton(child: Text("Start timer"), onPressed: () {

                  _startTimer();

                },),

              ],

            ),

          ),

        )

    );

  }

  Future connect(String address) async {

    try {

      connection=await BluetoothConnection.toAddress(address);

     // sendData('111');

      //durum="Connected to the device";

    } catch (exception) {

      // durum="Cannot connect, exception occured";

    }

  }

  @override

  void debugFillProperties(DiagnosticPropertiesBuilder properties) {

    super.debugFillProperties(properties);

  }

// --------------**************data gonder

  //Future send(Uint8List data) async {

    //connection.output.add(data);

   // await connection.output.allSent;

 // }

}

//------------*********** data gonder end

Arduino codes:

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

 char Buf[50]; //  to bluetooth device<------

String resistor_string="";

void setup() { 

 // hc-05 bluetooth module resistor-----------------------------

  // Open serial communications and wait for port to open:

  Serial.begin(9600);

  mySerial.begin(9600);

 }

void loop() {

   float volt_x=analogRead(A0);// Vin INPUT

   float volt_in=5*(volt_x/1023);

   float RX=(volt_in*100000)/(5-volt_in);  //------------>>>>>>  resistance formula

   float RX_divided=RX/1000;    // ohm ----> K OHM

     resistor_string=String(RX_divided);

       resistor_string=  resistor_string+" K ohm";

     resistor_string.toCharArray(Buf, 50);

     mySerial.write(Buf);

     delay(200);

}